1. Field of the Invention
The invention relates to spring carrier for mounting a spring strut to a vehicle, including a vibration damper including a cylinder and a piston rod which is axially guided in the cylinder, first and second spring collars with a spring therebetween, and an actuator which is driven to change the relative axial position of the spring collars.
2. Description of the Related Art
A vehicle chassis which comprises a spring carrier with an adjustable spring collar for a suspension spring is known from DE 102 55 764 B3, which represents the underlying state of the art. To actuate the spring collar, an actuator designed as an electric motor is used, which drives a hollow threaded spindle. A threaded nut is mounted on the actuating thread of the threaded spindle, and this nut is connected in turn to an adjustable spring collar. The rotary motion of the motor is converted by the combination of the spindle and the threaded nut into an axial motion of the spring collar. In the case of a passenger vehicle, for example, a suspension spring must support one-quarter of the entire load of the vehicle. The spring force is transmitted via the threaded nut/threaded spindle combination to the rotor and from there to the housing of the electric motor, which is connected by a resilient mount with both angular and impact resilience to a vehicle body.
A piston rod of a conventional vibration damper extends through the hollow threaded spindle. An axial bearing, which allows the piston rod a certain freedom of movement with respect to the vehicle body, is mounted on the outer end of the piston rod. The piston rod is attached to the mount by way of a cup-shaped component, against which the housing of the actuator is also supported. It follows from this that no relative movement can occur between the piston rod and the actuator.
The high-frequency damping forces which occur in the vibration damper are transmitted via the resilient mount to the vehicle body. Because of the spring forces which are present, the resilient mount is designed to be very stiff, with the result that the damping forces are transmitted almost unsprung to the vehicle body, where clearly audible noises occur.
Any transverse forces which the suspension spring may transmit to the threaded spindle are absorbed by the piston rod of the vibration damper, acting via a needle bearing. As a result, however, a transverse force is generated inside the vibration damper, which leads to an increase in the friction between the piston rod and the piston rod guide (not shown). As a result, the increase in static friction in the vibration damper leads to a loss of driving comfort.
Another disadvantage of this spring carrier is that it is very difficult to remove the vibration damper when it needs to be repaired. For this purpose, the entire spring carrier must be removed from the vehicle first. Then the housing with the stator and a lock washer can be removed so that then the piston rod can be pulled from the threaded spindle. On closer consideration, it is obvious that the installation of the vibration damper must also be rather complicated, because the thrust stop is peened onto the piston rod, and the threaded spindle has a much smaller inside diameter than the outside diameter of the thrust stop.